Determination Of Molecular Weight Distribution Research Articles

PolyWeight: A free and open-source program for determination of molecular weight distribution of linear polymers

This paper introduces PolyWeight, a Python software featuring a user-friendly graphical user interface (GUI), which offers two distinct approaches for MWD determination: an analytical relation-based method and a parametric model-based method. By utilizing dynamic moduli, users can calculate MWD as well as molecular weight averages such as Mn, Mw, and Mz. The functionality of PolyWeight is validated using synthetic data and real data obtained from the literature, exhibiting good agreement. Log files and datasets used in this work are available on GitHub. Program summaryProgram Title: PolyWeightCPC Library link to program files:https://doi.org/10.17632/rn8t4mmvyd.1Developer's repository link:https://github.com/a-minotto/PolyWeightLicensing provisions: GPLv3Programming language: Python 3.xNature of problem: Analytical rheology enables the determination of molecular weight distribution (MWD) by solving inverse problems. The reptation theory establishes a liaison between the viscoelastic behavior and MWD, permitting the application of mathematical resolution methods like regularization and parameterization. PolyWeight offers two solutions: a parameterization-based method that assumes a generalized exponential distribution (GEX) for the MWD, and an analytical relationship-based method that utilizes the relaxation spectrum.Solution method: The analytical relationship-based solution incorporates a mathematical formulation that considers the relaxation spectrum obtained from the dynamic moduli using the NLREG software. The numerical integration of the relaxation spectrum is performed utilizing the integrate.quad function from the SciPy library. An optimization process is employed in the parametric solution to perform a multiobjective fit of the viscoelastic models to the dynamic moduli. The integrals in this case are also calculated using the integrate.quad package from the SciPy library. The optimization procedure utilizes the lmfit library, where a Minimizer object is created based on the optimization function and subsequently utilized with the minimize function, employing the default Levenberg-Marquardt algorithm for the fit.

Indirect determination of partial depolymerization reactions in dialdehyde celluloses (DAC) by gel permeation chromatography of their oxime derivatives

Owing to a supposed quantitative transformation, oximation of dialdehyde cellulose (DAC) with hydroxylamine hydrochloride is commonly employed in chemical DAC analysis, e.g., for the determination of the degree of oxidation (DO) by titration or elemental analysis. In this study, this modification was utilized for the indirect determination of molecular weight distributions (MWD) by gel permeation chromatography (GPC). The presumably quantitative conversion of aldehyde groups in DAC to the corresponding oxime also breaks up the intermolecular and intramolecular hemiacetal crosslinks, which were associated with solubility issues in the DMAc/LiCl solvent system in previous studies. The limits of the procedure and the material's stability during oximation were investigated. For samples with a DO up to approximately 9% a good applicability was observed, before at higher DO values residual crosslinks led to solubility problems. The oximation/GPC protocol was used to examine the development of the MWD in the early stages of DAC formation under different reaction conditions. The time-dependent partial depolymerization of the polymer backbone was observed. Furthermore, the stability of DAC towards different pH conditions ranging from strongly acidic to strongly alkaline was tested. The depolymerization of DAC in alkaline media occurred with concomitant degradation of aldehyde moieties. In turn, DAC proved to be remarkably stable in acidic and neutral solutions up to a pH of 7.

A Novel Method for Dynamic Molecular Weight Distribution Determination in Organometallic Catalyzed Olefin Polymerizations

In this study, a mathematical model for the time evolution of molecular weight distribution (MWD) was developed. This temporal model is based on the well-known Ziegler–Natta polymerization mechanism and reaction kinetics by the parametric solving of related differential equations. However, due to the generality of the reactions involved, the model can be extended to the other type of catalysts, such as metallocenes, Phillips, etc. The superiority of this model lies in providing the possibility of a more precise prediction over the active sites and kinetic parameters using a simple mathematical equation, which leads to improved reactor design in large-scale production. The model uses a function to develop a methodology for MWD calculations. In this way, the transient response is limited to the first few minutes of the reaction; however, it is important as it demonstrates the establishment of the final MWD. According to the results, almost for practical conditions with negligible transfer resistances, the time dependency of the MWD has a transient interval, depending on the kinetic constants of polymerization reactions. Increasing the time to infinity results in an increase in MW and a widening in MWD, which confirms the experimental plots well. In short, the main advantage of our proposed model over the previous ones is its ability to predict the MWD even before the completion of the polymerization reaction. The results of the present model match well with those of the well-known Schulz–Flory distribution, which only predicts the final molecular weight distribution, thus confirming that the model is reliable and generalizable.

In-Situ Analysis of Anionic Coordination Polymerizations by Electrospray-Ionization Mass Spectrometry.

Anionic coordination polymerizations proceed via highly reactive intermediates, whose in situ analysis has remained difficult. Here, we show that electrospray-ionization mass spectrometry is a promising method to obtain detailed information on the polymerization process. Focusing on polymerization reactions of 1,3-dienes initiated by CoCl2 /RLi (R=Me, nBu, tBu, Ph), we directly observe the growing polymer chains and characterize the active anionic cobalt centers by gas-phase fragmentation experiments. On the basis of these results, we suggest a plausible mechanism for the polymerization reaction. Moreover, the ESI mass spectra permit the determination of molecular weight distributions, which are in good agreement with those derived from NMR-spectroscopic as well as MALDI mass-spectrometric measurements, and afford a wealth of kinetic data.

Colorimetric assay for the determination of molecular weight distribution and branching characteristics of starch hydrolysates

Here, we present a gold nanoparticle-based colorimetric assay for the determination of molecular weight distribution and branching characteristics of enzymatically hydrolyzed starch. The steric stabilization effect of starch hydrolysate on the colloidal stability of AuNPs was found to be proportional to the ratio of high molecular weight amylopectins, which was clearly reflected by the intensity of the characteristic surface plasmonic resonance (SPR) absorbance peak of the AuNPs. The fractional change of high molecular weight amylopectin over the course of enzymatic hydrolysis reaction could be measured based on the intensity of SPR peak, in which the results correlated well with those obtained by conventional gel permeation chromatography. With the proper calibration of a specific set of enzyme and starch type, this method would provide a fairly simple and fast means of analyzing the molecular weight distribution of starch hydrolysate on site as well as the amylose content in native starch.

Use of the Extended Fujita method for representing the molecular weight and molecular weight distributions of native and processed oat beta-glucans

Beta 1–3, 1–4 glucans (“beta-glucans”) are one of the key components of the cell wall of cereals, complementing the main structural component cellulose. Beta-glucans are also an important source of soluble fibre in foods containing oats with claims of other beneficial nutritional properties such as plasma cholesterol lowering in humans. Key to the function of beta-glucans is their molecular weight and because of their high polydispersity - molecular weight distribution. Analytical ultracentrifugation provides a matrix-free approach (not requiring separation columns or media) to polymer molecular weight distribution determination. The sedimentation coefficient distribution is converted to a molecular weight distribution via a power law relation using an established procedure known as the Extended Fujita approach. We establish and apply the power law relation and Extended Fujita method for the first time to a series of native and processed oat beta-glucans. The application of this approach to beta-glucans from other sources is considered.

Direct determination of molecular weight distribution of calf-thymus DNAs and study of their fragmentation under ultrasonic and low-energy infrared irradiations. A charge detection mass spectrometry investigation.

Calf-thymus (CT-DNA) is widely used as a binding agent. The commercial samples are known to be "highly polymerized DNA" samples. CT-DNA is known to be fragile in particular upon ultrasonic wave irradiation. Degradation products could have dramatic consequences on its bio-sensing activity, and an accurate determination of the molecular weight distribution and stability of commercial samples is highly demanded. We investigated the sensitivity of charge detection mass spectrometry (CDMS), a single-molecule MS method, both with single-pass and ion trap CDMS ("Benner" trap) modes to the determination of the composition and stability (under multiphoton IR irradiation) of calf-thymus DNAs. We also investigated the changes in molecular weight distributions in the course of sonication by irradiating ultrasonic waves to CT-DNA. We report, for the first time, the direct molecular weight (MW) distribution of DNA sodium salt from calf-thymus revealing two populations at high (~10MDa) and low (~3MDa) molecular weights. We evidence a transition between the high-MW to the low-MW distribution, confirming that the low-MW distribution results from degradation of CT-DNA. Finally, we report also IRMPD experiments carried out on trapped single-stranded linear DNAs from calf-thymus allowing extraction of their activation energy for unimolecular dissociation. We show that single-pass CDMS is a direct, efficient and accurate MS-based approach to determine the composition of calf-thymus DNAs. Furthermore, ion trap CDMS allows us to evaluate the stability (both under multiphoton IR irradiation and in the course of sonication by irradiating ultrasonic wave) of calf-thymus DNAs.

Stop-flow reversed phase liquid chromatography × size-exclusion chromatography for separation of peptides

Size-exclusion chromatography (SEC) with wide application in peptide analysis presents challenges in determination of molecular weight distribution due to the relatively low resolution. In this study, a stop-flow reversed phase liquid chromatography (RPLC) × SEC system was constructed, aiming at improving the peptide separation in SEC. As the chromatographic dispersion during stop-flow operation might contribute to the band broadening in the first dimension (1st D) RPLC, the effects of different stop-flow operational parameters on the additional band broadening were quantitatively evaluated. Unlike analytes of large molecular size or long retention time with low effective diffusion coefficient (Deff), additional band broadening was evidently observed for analytes of small molecular size and short retention time (high Deff). Therefore, optimal flow rate, low column temperature and short stop-flow time were suggested for analyzing small molecules of short retention time. The established stop-flow two-dimensional liquid chromatography (2D-LC) was further tested on protein hydrolysates. The resolution was evidently improved for both heart-cutting and comprehensive 2D-LC analysis (despite additional band broadening in RPLC). Compared with heart-cutting analysis with higher 1st D resolution for selective fractions, comprehensive analysis could provide more complete information about the molecular weight distribution of the eluting solutes along RPLC.

Diffusion in Polymer Solutions: Molecular Weight Distribution by PFG‐NMR and Relation to SEC

Quantification of diffusion coefficient distribution (DCD) and correlation with molecular weight distribution (MWD) of polymers is still an issue in pulsed field‐gradient nuclear magnetic resonance (PFG‐NMR). The conventional scaling law utilized so far to relate diffusion coefficient and molecular weight only holds true for the determination of MWD at sufficiently low concentrations. To extend measurement limits and to get a good signal‐to‐noise ratio, an exponential correlation is introduced to describe the effect of polymer concentration on diffusion in PFG‐NMR. Two model polymers (polystyrene and poly(methyl methacrylate)) dissolved in deuterated chloroform are studied at different concentrations in the range of 0.16–8 wt%. The DCDs are determined by modeling the measured signal attenuation with three methods (gamma distribution, log normal distribution, and tailored norm regularization). It is shown that the proposed method applies to the PFG‐NMR measurements on polymer solutions over a wide concentration range, providing almost the same MWDs as those obtained at low concentrations. The MWDs retrieved from NMR experiments agree well with those by size exclusion chromatography. image

Extraction, molecular weight distribution, and antioxidant activity of oligosaccharides from longan (Dimocarpus Longan Lour.) pulp.

Ultrasonic-microwave synergistic extraction (UMSE) was optimized for the extraction of oligosaccharides from longan pulp (OLP). Box-Behnken design was used to evaluate the effects of temperature (35-55°C), ultrasonic time (5-25 min), and water to material ratio (10-30 mL/g) on the extraction efficiency of crude OLP. A regression model was developed and its validity was statistically demonstrated. Significant interaction between temperature and water to material ratio was observed. The following optimal conditions for the extraction yield of crude OLP were determined: extraction temperature 55°C, ultrasonic time 18.52 min, and water to material ratio 10 mL/g. The extracted OLP were purified for the determination of molecular weight distribution and antioxidant activity. Results of matrix-assisted laser desorption ionization time-of-flight mass spectrometry revealed that the molecular weight distribution of the purified OLP ranged from m/z 495.138 to 795.511. The purified OLP exhibited a dose-dependent behavior in 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity.

Molecular Weight Determination of Palm Olein Polyols by Gel Permeation Chromatography Using Polyether Polyols Calibration

AbstractNatural oil polyols have been intensively developed and successfully used for the production of various polymers, notably polyurethanes. The need to access the average molecular weight (MW) and the MW distribution (MWD) has led to the efforts to have a precise and reliable determination method. A series of commercial polyether polyols, with well‐defined MW, was used as a gel permeation chromatography (GPC) calibration standard to determine the MW of palm olein polyols. This GPC analysis was compared to the one calibrated against the commercially available polystyrene (PS) standards and to the number‐average molecular weight (Mn) obtained via vapor pressure osmometry (VPO) technique. For example, the Mn obtained for palm olein polyol E‐135 calibrated against polyether polyols was 2,537 Da, which was closer to the Mn via VPO (1,618 Da), than the Mn obtained using PS as calibration standards (3,836 Da). Hence, this GPC analysis using polyether polyols as calibration standards can offer reassured determination of MWD of palm olein polyols.

Determination of molecular weight distribution and composition dependence of monomeric friction factors from the stress relaxation of ultrahigh molecular weight polyethylene gels

The stress relaxation of ultrahigh molecular weight polyethylene (UHMWPE) gels in a broad composition range ( 0.025≤ϕP≤1.0) was studied within the framework of the reptation model. The molecular weight distribution (MWD) was determined at an optimum gel concentration ( ϕP=0.365) by regularization analysis of the stress relaxation data. The calculated relaxation moduli [ G(t)] by using MWD evaluated at a certain composition (UHMWPE gels, ϕP=0.365) were consistent with the experimental G(t) of other compositions in a broad range ( 0.218≤ϕP≤1.0). That is, the MWD (regularization method) was self-consistent within the framework of the reptation model. The composition dependence of the monomeric friction factor ( ζeff) of the UHMWPE gels was examined by use of the double reptation (DR) model with the determined MWD. The Ferry's free volume model of the molecular weight dependence of ζeff can be extended to the composition dependence of ζeff. In the low-concentration gels ( 0.025≤ϕP≤0.17), the experimental G(t)...

Polyether polyols as GPC calibration standards for determination of molecular weight distribution of polyether polyols

ABSTRACTAverage molecular weights (Mn,MwandMp) are important characteristics of oligomers and polymers, and therefore there is a need to have a precise and reliable determination method. A gel permeation chromatography (GPC) coupled with a single refractive index detector was used to determine the molecular weight distributions of commercial polyether polyols calibrated against a series of polyether polyols with known molecular weights and low polydispersity. Results of these GPC analyses were compared to the ones calibrated against the commercially available polystyrene (PS) standards. The number‐average molecular weights (Mn) obtained with GPC using polyether polyols calibration were closer to the theoretical values than theMnobtained using PS as calibration standards. Hence, these GPC analyses using polyether polyols as calibration standards can provide reliable determination of molecular weight distribution of polyether polyols and can be potentially applied to natural oil‐based polyols, including palm oil‐based polyols. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2015,132, 42698.

Molecular weight distribution of asphaltic paving binders from phase-angle measurements

Based on previous works on polymers and regular bitumens, a new method for determining the molecular weight distribution (MWD) of asphaltic paving binders, using the phase angle () of the complex modulus measured in the linear viscoelastic domain, has been developed in this paper. MWDs of pure petroleum bitumens, natural bitumens, modified bitumens and artificially aged bitumens are calculated by this method and compared with MWDs obtained by gel permeation chromatography. The two methods give comparable results, but the δ-method developed here is more sensitive to the molecular weight of species. This method is very simple to implement, and seems a powerful tool in the determination of MWD of bitumens, in the visualisation and repartition of modifiers in the bitumen matrix and in the ageing monitoring and quantification.

Determination of molecular weight distributions in native and pretreated wood.

The analysis of native wood components by size-exclusion chromatography (SEC) is challenging. Isolation, derivatization and solubilization of wood polymers is required prior to the analysis. The present approach allowed the determination of molecular weight distributions of the carbohydrates and of lignin in native and processed woods, without preparative component isolation steps. For the first time a component selective SEC analysis of sawdust preparations was made possible by the combination of two selective derivatization methods, namely; ionic liquid assisted benzoylation of the carbohydrate fraction and acetobromination of the lignin in acetic acid media. These were optimized for wood samples. The developed method was thus used to examine changes in softwood samples after degradative mechanical and/or chemical treatments, such as ball milling, steam explosion, green liquor pulping, and chemical oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). The methodology can also be applied to examine changes in molecular weight and lignin-carbohydrate linkages that occur during wood-based biorefinery operations, such as pretreatments, and enzymatic saccharification.

USP compendial methods for analysis of heparin: chromatographic determination of molecular weight distributions for heparin sodium.

USP compendial methods for analysis of heparin: chromatographic determination of molecular weight distributions for heparin sodium.

The use of Gauss-Hermite quadrature in the determination of the molecular weight distribution of linear polymers by rheometry

The molecular weight distribution (MWD) and its parameters are of the fundamental importance in the characterization of polymers. Therefore, the development of techniques for faster MWD determination is a relevant issue. This paper aims at implementing one of the relaxation models from double reptation theory proposed in the literature and analyzing the numeric strategy for the evaluation of the integrals appearing in the relaxation model. The inverse problem, i.e., the determination of the MWD from rheological data using a specified relaxation model and an imposed distribution function was approximated. Concerning the numerical strategy for the evaluation of the integrals appearing in the relaxation models, the use of Gauss-Hermite quadrature using a new change of variables was proposed. In the test of samples of polyethylene with polydispersities less than 10, the application of this methodology led to MWD curves which provided a good fit of the experimental SEC data.

A “Systematic Approach” to TD‐GPC Data Processing with Band Broadening Correction

SummaryThe application of the systematic approach during detector offset determination in triple detector GPC polymer analysis has been shown to result in improvements in terms of the variations observed among the methods for molecular weight distribution determination. More importantly, the remaining, reduced variations are theoretically consistent with axial dispersion corrections proposed in the past. The use of the systematic approach for offset determination coupled with a robust axial dispersion correction offers the potential for completely reconciling the molecular weight results obtained from the three available methods of molecular weight determination in triple detector GPC.

Influence of the degree of hydrolysis (DH) on antioxidant properties and radical-scavenging activities of peanut peptides prepared from fermented peanut meal

To study the influence of degree of hydrolysis (DH) on antioxidant properties of peanut peptides, the peanut meal was fermented by Bacillus subtilis. The fermentation time was 48, 72, and 96 h, respectively, to prepare peanut peptides at different degree of hydrolysis. The peanut peptides (11.18, 16.20, and 21.41% of DH, respectively) were extracted from fermentation liquid. The antioxidant properties of these peanut peptides were evaluated based on DPPH· radical (1,1-Diphenyl-2-picrylhydrazyl radical) scavenging activity, superoxide anion-scavenging activity, reducing power, metal-chelating activity, and inhibition of linoleic acid autooxidation. Peanut peptides (21.41% of DH) at 1 mg/mL exhibited 80.86 and 29.35% of scavenging concentration percent on DPPH· and superoxide anion radical, respectively. In addition, the reducing power of peanut peptides was 0.368 at 2 mg/mL, and they possessed 76.32% of Fe2+-chelation ability at 2 mg/mL and 63.75% of inhibition of linoleic acid autooxidation at 0.8 mg/mL. The antioxidant activities of the peanut peptides (21.41% of DH) were stronger compared with others (11.18 and 16.20% of DH), and this indicated the antioxidant activities of peanut peptides increased with increasing DH (p < 0.05). To know much about the peanut peptides, they were subjected to amino acid analysis and determination of molecular weight distribution. Some acidic amino acids and essential amino acids were found, and the average molecular weight distributions were concentrated in <1,400 Da (86.96%). Combined with the results of the amino acid profiles, the peanut peptides were believed to have high nutritive value besides antioxidant activities.

Amino acid composition, molecular weight distribution and antioxidant activity of protein hydrolysates of soy sauce lees

The proteins of soy sauce lees (SSLP) were hydrolysed by Alcalase in the presence of ultrasound or traditional water bath to obtain hydrolysates S2–S6. The analysis of protein content indicated that enzymatic hydrolysis could significantly improve the extraction efficiency of proteins. By determination of molecular weight distribution, >10 and 5–10 KDa fractions of native SSLP (S1) decreased during hydrolysis, whilst 3–5 KDa fraction increased. Gradual increases of free, total and antioxidant amino acids were observed for S1–S4, and the differences between S4 and S6 were slight. Tyrosine was the major free amino acid of S1–S6, whilst glutamic acid had the highest amount in total amino acid composition. S2–S6 showed stronger DPPH radical scavenging activities in a dose-dependent manner than S1. All the results suggested that ultrasound treatment showed an inhibition behaviour on the enzymatic hydrolysis of SSLP.